1. Field of the Invention
The present invention relates to an image stabilization control circuit used for an image pickup apparatus.
2. Description of the Related Art
In recent years, the quality of images handled by image pickup apparatuses such as digital still cameras and digital video cameras has been enhanced by increasing the number of pixels handled by an imaging element installed in the device. Another desired method for enhancing the quality of images captured by image pickup apparatuses involves providing the image pickup apparatuses with a hand-shake correction function in order to prevent blurring of a target image due to vibration generated when the hand(s) holding the image pickup apparatus shake or for other reasons.
Specifically, the image pickup apparatus comprises a vibration-detecting element such as a gyro-sensor. The device drives moveable components such as a corrective lens or an imaging element, according to an angular velocity component generated by vibration of the image pickup apparatus; and prevents the image from blurring. A high-quality image signal with no blurring can thereby be obtained without the vibration component reflected in the resulting imaging signal, even if the image pickup apparatus vibrates.
FIG. 4 is a block diagram of a conventional image stabilization control circuit 100 for obtaining a hand-shake correction function. The image stabilization control circuit 100 is provided to an image pickup apparatus, and is operated under the control of a main control circuit (not shown) provided to the image pickup apparatus. The image stabilization control circuit 100 is connected to a position-detecting element 102, a lens-driving element 104, and a vibration-detecting element 106.
The position-detecting element 102 detects the position of a corrective lens (lens 108) that constitutes a part of an optical system of the image pickup apparatus. The position-detecting element 102, which may be a Hall element, generates an induced current according to the absolute position of the lens 108, and outputs a voltage signal. The lens-driving element 104 may be a voice coil motor. The image stabilization control circuit 100 adjusts the magnitude of a voltage applied to the lens-driving element 104 and thereby controls the position of a moveable coil in the voice coil motor; i.e., the position of the lens 108. The lens-driving element 104 drives the lens 108 within a plane (x-y plane) perpendicular to an optical axis of the image pickup apparatus. The vibration-detecting element 106 detects vibration of the image pickup apparatus and outputs the result to the image stabilization control circuit 100. The vibration-detecting element 106 may be a gyro-sensor. The vibration-detecting element 106 generates an angular velocity signal corresponding to the vibration imparted to the image pickup apparatus, and outputs the signal to the image stabilization control circuit 100.
Each of the position-detecting element 102, the lens-driving element 104, and the vibration-detecting element 106 preferably comprises at least two elements. For example, a plurality of elements are provided so as to correspond to the direction of each of the x-axis and the y-axis, the elements detecting the position of the lens 108, moving the lens 108, and detecting vibration of the image pickup apparatus.
The image stabilization control circuit 100 will now be described in detail. The image stabilization control circuit 100 has a servo circuit 10, a lens driver 12, an analog-digital converter circuit (ADC) 14, a central processing unit (CPU) 16, and a digital-analog converter circuit (DAC) 18.
The servo circuit 10 generates a signal for controlling the lens-driving element 104 according to a voltage signal outputted by the position-detecting element 102. The servo circuit 10 has an analog filter circuit having an external resistor, capacitor, or another component; and generates a signal for controlling the lens-driving element 104 so as to counteract a displacement in an image caused by tilting of an optical axis of the lens of the image pickup apparatus. Based on the signal generated by the servo circuit 10, the lens driver 12 generates a lens-driving signal for driving the lens-driving element 104.
The ADC 14 converts the analog angular velocity signal outputted by the vibration-detecting element 106 into a digital signal. Based on the digital angular velocity signal, the CPU 16 generates an angle signal indicating the degree of displacement of the image pickup apparatus. The CPU 16 is connected to a memory device (not shown), the CPU 16 generating the angular signal based on software stored in the memory device. The DAC 18 converts the digital angle signal generated by the CPU 16 into an analog signal.
The servo circuit 10 generates a lens-driving signal for driving the lens-driving element 104 according to a signal that is a sum of the analog angle signal outputted by the DAC 18 and the voltage signal outputted by the position-detecting element 102. Specifically, in order to prevent hand-shake-derived blur, the position of the lens is altered based on the angle signal indicating the degree of displacement of the image pickup apparatus, and blurring of the target image on the imaging element is prevented. Hand-shake-derived blur of the target image is thereby minimized, and a high-quality image signal can be obtained.